Hydrocarbon exploration includes drilling operations that seek to recover hydrocarbon deposits from below the Earth's surface. Typically, a drilling rig is used to drill a wellbore (straight and/or directional) that provides access to a subsurface formation. In addition, a drilling rig may be used to stimulate an existing well and gain access to more remote subsurface formations. Hydraulic fracturing is an example of an effective well-stimulation technique in which a geologic formation is hydraulically fractured by a high-pressure fluid to extract the hydrocarbon deposits disposed therein.
Conventional drilling methods include the use of a top drive, or rotary table, drilling system that is configured to rotate a drill string and a drill bit from the surface or the use of a hydraulic drilling system that is configured to rotate a drill bit downhole using hydrostatic pressure. In certain applications, more than one drilling method may be used at different times during the course of drilling operations. For example, a top drive drilling system may be used to establish a substantially vertical wellbore and a hydraulic drilling system may be used as part of slide drilling operations to drill in a directional manner. Because of advances in directional drilling and well-stimulation techniques, more remote subsurface formations are now accessible for hydrocarbon recovery.
A conventional hydraulic drilling system includes a hydraulic power section, sometimes referred to as a mud motor, which is disposed downhole to convert hydraulic energy from drilling fluid and/or drilling mud into mechanical energy that rotates a drill bit. A conventional mud motor uses a Moineau progressive cavity positive displacement pump system that typically includes a helical rotor inserted into a double helix stator. The interference fit between the rotor and the stator forms a number of sealed cavities. As fluid enters a cavity formed at an inlet, hydrostatic pressure forces the fluid through the cavities toward an outlet and rotates the rotor eccentrically within the stator. The eccentric rotation of the rotor is transferred to the drill bit by a drive shaft assembly that seeks to reduce or eliminate eccentricity while transferring torque to the drill bit.